Chapter 9

Aldehydes and Ketones

Chemistry 20

Carbonyl group

C

=O

Aldehydes Ketones Carboxylic acids Esters

CH3COCH2CH3

ONaOH

H2OCH3CO-Na+

O

CH3CH2OH

Sodiumhydroxide

+ +

Ethyl acetate Sodiumacetate

Ethanolheat

• In an aldehyde, at least one H atom is attached to a carbonyl group.

• In a ketone, two carbon groups are attached to a carbonyl group.

Aldehydes and Ketones

C=O

Step 1Select the longest carbon chain

that contains the carbonyl group (C=O).

Step 2Number from the end nearest C=O group.

Step 3Change the ending of parent alkane from -e to -al.No number for carbonyl group C=O (it always comes first).

Step 4Give the location and name of each substituent

(alphabetical order) as a prefix to the name of themain chain.

Naming Aldehydes

• Common names for the first two aldehydes use the prefixes “form” (1C) and “acet” (2C) followed by “aldehyde”.

H─C─H CH3─ C ─H CH3─CH2─ C ─H methanal ethanal propanal(formaldehyde) (acetaldehyde)

Naming Aldehydes

=O =O =O

CH3─CH─CH2─ C─H 3-Methylbutanal

Cl─CH2─CH2─ C─H 3-Chloropropanal

CH3

1234

123

=O

=O

Step 1Select the longest carbon chain

that contains the carbonyl group (C=O).

Step 2Number from the end nearest C=O group.

Step 3Change the ending of parent alkane from -e to -one.

Use the number to show the location of C=O.

Step 4Give the location and name of each substituent

(alphabetical order) as a prefix to the name of themain chain.

Naming Ketones

Naming Ketones

• In the common name, name the “alkyl groups” alphabetically attached to the carbonyl group and add the word “ketone”.

CH3 ─ C ─CH3 CH3─C─CH2─CH3

Propanone 2-Butanone

(dimethyl ketone) (ethyl methyl ketone)

1 2 3 4

=O=O

O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

CH

O

Benzoic acidBenzaldehyde

+ O2

COH

O

2 2

3-ChloroO

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

CH

O

Benzoic acidBenzaldehyde

+ O2

COH

O

2 2

Cl

O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

O

Acetone 2-Methylcyclohexanone5-Methyl-3-hexanone

OO

12

34

56

12

O

H

OOH

NH2

3-Hydroxy-4-methylpentanal 3-Amino-4-ethyl-2-hexanone

1345 12346

O

H

OOH

NH2

3-Hydroxy-4-methylpentanal 3-Amino-4-ethyl-2-hexanone

1345 12346

O

H

OOH

NH2

3-Hydroxy-4-methylpentanal 3-Amino-4-ethyl-2-hexanone

1345 12346

O

H

OOH

NH2

3-Hydroxy-4-methylpentanal 3-Amino-4-ethyl-2-hexanone

1345 12346

3-Methylbutanal 2-Propenal(Acrolein)

Hexanal

12

34H

O

H

O1

23

45

6

123

H

O3-Methylbutanal 2-Propenal

(Acrolein)Hexanal

12

34H

O

H

O1

23

45

6

123

H

O

Physical properties of Aldehydes and Ketones

1. They have strong odors (ketones have pleasant odors).

2. They are polar compounds.

3. Only dipole-dipole interactions (no hydrogen bonding).

4. Low boiling points compare to amines and alcohols.

5. Soluble in water (no soluble in nonpolar compounds).

δ+

δ-

δ+

δ-H

OHδ+

Hydrogen bond with water.

Higher than hydrocarbons.

C-O 3.5-2.5 = 1

Chemical properties of Aldehydes and Ketones

1. Oxidation: only for aldehydes (not for ketones).

K2Cr2O7

H2SO4

CH3─CH2─CH2─CH2─C─OH

=

O

CH3─CH2─CH2─CH2─C─H

=

O

Pentanal Pentanoic acidK2Cr2O7: Oxidizing agent

CH

O

Benzoic acidBenzaldehyde

+ O2

COH

O

2 2Liquid aldehydes

are sensetive to oxidation.

No oxidizing agent

Tollen’s Test (Silver-mirror test)

R-C-HO

2Ag(NH3)2+ 3OH-

R-C-O-O

2Ag 4NH3 2H2O

+ +

+ + +

Tollens'reagent

Carboxylicanion

Silvermirror

Aldehyde

Tollens’ reagent is specific for the oxidation of aldehydes (not for ketones).

Chemical properties of Aldehydes and Ketones

2. Reduction:

Like reducing the alkene (C = C) to alkane (C – C):

– Reduction of an aldehyde gives a primary alcohol (-CH2OH).

– Reduction of a ketone gives a secondary alcohol (-CHOH-).

H2

tran sition

metal catalyst+

1-Pen tan ol

CH3─CH2─CH2─CH2─C─ H

=

O

PentanalCH3─CH2─CH2─CH2─CH2─ OH

H2

tran si tion

metal cataly st+CH3─C─CH2─CH3

=

O

CH3─CH─CH2─CH3

-OH

2-butanol2-butanone

O NaBH4O-

HH3O+ O-H

H

H - C O H C O - H3O+

H C O-H: +

Hydrideion

Chemical properties of Aldehydes and Ketones

Reduction mechanism:

NaBH4 Sodium borohydride: produces hydride ion: H-

-

Reducing agent

Reduction by NaBH4 does not affect a carbon-carbon double bond or an aromatic ring.

Advantage of NaBH4:

HCO

1. NaBH4

2. H2O

CH2OH

Cinnamaldehyde Cinnamyl alcohol

H3O+

Chemical properties of Aldehydes and Ketones

3. Addition of alcohols (hemiacetals):

CH

OO-CH2CH3

HC OCH2CH3

H

O-H+

Benzaldehyde Ethanol A hemiacetal

H of the alcohol adds to the carbonyl oxygen and

OR adds to the carbonyl carbon.

unstable

Chemical properties of Aldehydes and Ketones

Chemical properties of Aldehydes and Ketones

O-CH2CH3H C OCH2CH3

H

O CH2CH3

+

Ethanol An Acetal

C OCH2CH3

H

O-H

A hemiacetal

+H2OAcid

3. Addition of alcohols (Acetals):

H

O

O-HC

O O

H

H

O O-H

H

4-Hydroxypentanal A cyclic hemiacetal

123

45

1345

redraw to show the -OH and -CHO close

to each other2

3. Addition of alcohols (hemiacetals):

If –OH is part of the same molecule that contains C=O.

Chemical properties of Aldehydes and Ketones